My August 2002 build, '02 MINI Cooper CVT doesn't have a single rattle or noise in the cabin. Solid as they day we took delivery 6 months ago.
There are 4 factors as to why rattles may be prevalent on these cars:
1) The interior have lots and lots of plastic
2) Very stiff body structure
3) In the case of the
MCS, you have the stiffest SS+ suspension.
4) Stiff and rough riding Runflat tires.
It seems to me that owners of regular Coopers with the 15" non-runflat tires seem to have less problems or complaints about interior squeaks and rattles.
Our MINI does not have runflat tires or the SS+ suspension...does this help minimize rattles...maybe so.